Dental Age Classes in Marmosa incana and Other Didelphoids

Abstract

The tooth eruption and replacement sequence in Marmosa incana does not follow that described by Tyndale-Biscoe and Mackenzie (1976) for Didelphis marsupialis; therefore, a modified system of dental age classes is proposed. Whereas, in Didelphis the first or deciduous molar (herein referred to as dP3) is shed and P3 erupts before the appearance of M4, in M. incana dP3 is retained until M4 is functional; four molariform teeth, therefore, are present at all times from class 4 onward. The same sequence occurs in many species of Marmosa (sensu lato), Monodelphis, and Caluromys, whereas the Didelphis pattern is followed by species of Philander, Chironectes, Lutreolina, and the microbiotheriid Dromiciops. The sequence in Metachirus is somewhat ambiguous. A possible inference is that Marmosa and Monodelphis belong with Caluromys in a monophyletic group, rather than with the other didelphids.